Regulation of IGF-I mRNA and signal transducers and activators of transcription-3 and -5 (Stat-3 and -5) by GH in C2C12 myoblasts

Endocrinology. 2002 Feb;143(2):492-503. doi: 10.1210/endo.143.2.8641.

Abstract

GH and IGF-I are critical hormones for the regulation of longitudinal growth and the maintenance of lean body mass in humans. The regulation of IGF-I expression by GH in hepatocytes is well documented; however less is known about the regulation of IGF-I in peripheral tissues such as muscle. We have examined the regulation of IGF-I mRNA by GH and IGF-I in C2C12 myoblasts. GH stimulated the accumulation of IGF-I mRNA dose- and time-dependently. An elevation of IGF-I mRNA was observed with GH doses as low as 0.75 ng/ml and after exposure to GH for as little as 1 h, and the increase required ongoing transcription and translation. GH applied in a pulsatile fashion for 10 min followed by an 8-h interpulse interval increased IGF-I mRNA to a greater extent than continuous exposure. GH stimulated tyrosine phosphorylation of the GH receptor, signal transducer and activator of transcription-3 (Stat3), and Stat5. Stat5 was resistant to additional phosphorylation if cells were given a GH pulse within 2 h of a previous GH exposure. The refractory period lasted for 4 h, and cells could be maximally stimulated again after 6 h. Stat3 phosphorylation was also enhanced in cells that were allowed to recover from a previous application of GH. The tyrosine kinase inhibitors, genistein, PP1, and AG-490, and the MAPK kinase inhibitor, PD98059, did not block Stat3 or Stat5 phosphorylation. In contrast, WHI-P154, a Janus kinase-3 inhibitor, dose-dependently prevented Stat3, but not Stat5, phosphorylation. GH-inducible nuclear transport of Stat3 was likewise inhibited by WHI-P154. Most importantly, GH-dependent IGF-I mRNA expression was inhibited by WHI-P154. In contrast, IGF-I mRNA expression was inhibited by IGF-I peptide, and the effect of IGF-I was dominant over that of GH. IGF-I mRNA was regulated by both PI3K and MAPK signal transduction pathways, but IGF-I peptide signaled predominantly through a wortmannin-sensitive pathway to down-regulate its own mRNA. Our data suggest that Janus kinases (Jak2 or Jak3) and their downstream targets (Stat3 and Stat5) may play important roles in the expression of IGF-I mRNA and the myoblast response to GH. In addition, C2C12 cells appear to be a good model system to examine GH regulation of Janus kinase/Stat signaling and the regulation of IGF-I mRNA.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Blotting, Northern
  • Blotting, Western
  • Cell Line
  • DNA-Binding Proteins / biosynthesis*
  • DNA-Binding Proteins / genetics
  • Enzyme Inhibitors / pharmacology
  • Human Growth Hormone / antagonists & inhibitors
  • Human Growth Hormone / pharmacology*
  • Humans
  • Insulin-Like Growth Factor I / biosynthesis*
  • Insulin-Like Growth Factor I / genetics*
  • Janus Kinase 3
  • Mice
  • Milk Proteins*
  • Muscle, Skeletal / cytology
  • Muscle, Skeletal / metabolism
  • Phosphorylation
  • Precipitin Tests
  • Protein-Tyrosine Kinases / antagonists & inhibitors
  • Quinazolines / pharmacology
  • RNA, Messenger / biosynthesis*
  • RNA, Messenger / genetics*
  • RNA, Messenger / isolation & purification
  • STAT3 Transcription Factor
  • STAT5 Transcription Factor
  • Signal Transduction / drug effects*
  • Trans-Activators / biosynthesis*
  • Trans-Activators / genetics
  • Transcriptional Activation / drug effects

Substances

  • DNA-Binding Proteins
  • Enzyme Inhibitors
  • Milk Proteins
  • Quinazolines
  • RNA, Messenger
  • STAT3 Transcription Factor
  • STAT3 protein, human
  • STAT5 Transcription Factor
  • Stat3 protein, mouse
  • Trans-Activators
  • WHI P154
  • Human Growth Hormone
  • Insulin-Like Growth Factor I
  • Protein-Tyrosine Kinases
  • JAK3 protein, human
  • Jak3 protein, mouse
  • Janus Kinase 3